Typically an illumination apparatus includes a plurality of light sources, differing from one another in terms of light-emission color, in order that the illumination apparatus emits light of a desired light-emission color which is a mixture of light emitted from each of the light sources.
FIG. 18 is a circuit diagram of an illumination apparatus disclosed in Japanese Unexamined Patent Application Publication No. 2009-302008. In FIG. 18, an illumination apparatus 910 includes a light emitting diode (LED) group 903a that emits yellow light, an LED group 903b that emits green light, an LED group 903c that emits blue light, an LED group 903d that emits red light, and a lighting device 902 that lights the LED groups 903a, 903b, 903c, and 903d. The lighting device 902 includes a direct current (DC) power supply circuit 901, fixed current circuits 905a, 905b, 905c and 905d (herein, referred to as fixed current circuits 905 when differentiation is not necessary), and a control circuit 906. The fixed current circuits 905 each have the same structure and each include a switching element Q905 and a resistant element R905.
Each of the fixed current circuits 905 is connected in series to a corresponding one of the LED groups 903a, 903b, 903c, and 903d. The LED groups 903a, 903b, 903c, and 904d are connected in parallel to one another with respect to the DC power supply circuit 901. The lighting device 902 performs pulse width modulation (PWM) control of the switching element Q905 included in the fixed current circuit 905a in order to adjust a duty cycle of the switching element Q905. The above configuration enables the lighting device 902 to adjust magnitude of current flowing through the LED group 903a and thus also adjust brightness of the LED group 903a. The PWM control and lighting is performed in the same way for each of the LED groups 903b, 903c, and 903d, enabling the lighting device 902 to adjust brightness of each of the LED groups 903b, 903c, and 903d. Chromaticity of mixed light emitted collectively from the LED groups 903a, 903b, 903c, and 903d can be adjusted to a desired chromaticity through adjustment of a ratio of the LED groups 903a, 903b, 903, and 903d relative to one another, in terms of brightness thereof.
Note that during PWM control by the control circuit 906, the switching elements Q905 in the fixed current circuits 905 are each switched on at the same timing, but the switching elements Q905 are each switched off individually at a timing in accordance with a duty cycle which is determined for the corresponding switching element Q905. As a result, on-periods of the switching elements Q905 in the fixed current circuits 905, each of which holds the corresponding switching element Q905 in a switched-on state, may be overlapped with one another.
The LED groups 903a, 903b, 903c, and 903d each include the same number of LED chips. Note that when current of the same magnitude flows through the LED chips of different emission colors, the LED chips may have different forward voltages from one another due to differences in layer structure and light-emitting layer material of the LED chips. In such a situation, when current of the same magnitude flows through the LED groups 903a, 903b, 903c, and 903d, the LED groups 903a, 903b, 903c, and 903d have different voltage drops from one another. In the illumination apparatus 910, each of the LED groups 903a, 903b, 903c, and 903d is connected in series to a resistant element R in order to compensate for the voltage drop. Through the above configuration, even when the respective on-periods of the switching elements Q905 in the fixed current circuits 905 are overlapped with one another, current concentration is avoided in an LED group having the smallest voltage drop among the LED groups 903a, 903b, 903c, and 903d, thereby enabling appropriate current to flow in each of the LED groups 903a, 903b, 903c, and 903d. 
In order to individually compensate for the voltage drop of each light source, a conventional illumination apparatus such as described above includes resistant elements that are each connected in series to a corresponding one of the light sources. As a consequence, during lighting of the light sources in the conventional illumination apparatus, electric power is disadvantageously consumed in the resistant elements, which are each connected in series to the corresponding light source in order to individually compensate for the voltage drop across the light source.